MXPA99010202A - Epoxidation process using a phosphate-stabilized peroxotungstate compound as catalyst - Google Patents

Abstract

Olefins are selectively converted to epoxides using hydrogen peroxide as oxidant in a single liquid phase reaction system characterized by a liquid phase comprised predominantly of an organic solvent. The reaction is catalyzed by a compound comprised of a phosphate-stabilized peroxotungstate species having a W:P atomic ratio of 2:1.

Description

EPOXIDATION PROCESS USING A STABILIZED PEROXOTUNGSTATE COMPOUND AS CATALYST FIELD OF THE INVENTION This invention relates to methods of olefins converted to epoxides in a single liquid phase using hydrogen peroxide and a catalyst in salt or acid form comprising a species corresponding to [PW2O-3 (OH)] "2 BACKGROUND OF THE INVENTION U.S. Patent No. 5,274,140, describes a process for olefin epoxidation by reaction with hydrogen peroxide according to a double phase technique (ie, a biphasic reaction system containing both an aqueous phase as an organic phase.) The catalyst system consisting of a first component that is at least one element selected from W, Mo, V or a derivative thereof, and a second component that is at least one derivative selected from the derivatives of P and As. The mutual atomic ratio of the catalyst components is between 12 and 0.1, but preferably between 1.5 and 0.25 US Patent Nos. 4,562,276 and 4,595,671 describe n epoxidation catalysts for olefinic compounds, both in the homogeneous aqueous phase as well as in the heterogeneous phase. The catalyst corresponds to the formula Q3XW4O24_2n where Q represents a cation and an anionic salt, X is P or A, while n = 0, 1 or 2. The atomic ratio of W: P, where X = P, therefore , may be 4. The use of said compositions in an epoxidation wherein the reagents are maintained in a single substantially organic phase is not described. The Patent of E.U.A. No. 5,324,849, teaches a class of compounds based on tungsten and diphosphonic acids containing active oxygen atoms and cationic groups derived from onium salts. Said compounds are such that they catalyze the olefin oxidation reactions in double phase reaction systems containing both an organic phase and an aqueous phase. The compounds contain two phosphorous atoms and five tungsten atoms and, therefore, have an atomic ratio of W: P of 5: 2. Biphasic reaction systems of the type described in the patents mentioned above have a number of disadvantages which, however, limit their use in large-scale commercial practice. The need to use a phase transfer agent contributes significantly to the cost of operation. Mass transfer problems are often encountered, particularly for relatively volatile olefins such as propylene. Additionally, the engineering difficulties associated with the operation of two-phase reactors and phase separators can be considerable. Therefore, there is a need to develop active catalysts capable of providing high selectivity to the epoxide during the operation of a single phase epoxidation process.

SUMMARY OF THE INVENTION This invention provides a process for the epoxidation of an olefin comprising contacting the olefin with hydrogen peroxide in a substantially single phase liquid organic reaction system in the presence of a catalytically effective amount of a compound in the form of salt or acid comprising a species corresponding to [PW2O? 3 (OH)] "2 for a time and at an effective temperature to form an epoxide corresponding to the olefin DETAILED DESCRIPTION OF THE INVENTION The compounds used as the catalyst in the process of epoxidation of this invention comprising a species corresponding to the empirical formula [PW2O? 3 (OH)] "R This species is characterized as having a W: P atomic ratio of 2: 1 and can be described as a stabilized phosphate peroxotungstate . The compound may be in the form of an acid or salt. The cationic portion of the compound is not critical and can be any positively charged species in an amount sufficient to provide overall neutrality of the compound. In a particularly preferred embodiment of the invention, however, the compound has the empirical formula Y (2-x * [PW2O? 3 (OH)] wherein Y is H +, alkylammonium or combinations thereof, x = O when Y is a monocation, and x = 1 when Y is a dication, the identity of Y may be suitably varied to impart the desired solubility characteristics to the compound.Alkylammonium cations are generally selected when the solubilization of the salt in the liquid single-phase reaction system is desired. Suitable alkyl ammonium species are those positively charged nitrogen species having at least one alkyl group attached to nitrogen, More preferably, Y is a quaternary ammonium species corresponding to NR1R2R3R4 wherein Ri, R2, R3 and R4 are the same or different and are selected from the C? -C24 alkyl groups, and can also be a species of dicoutary ammonium containing two tetrasubstituted nitrogen atoms. ios a [PW2O? 3 (OH)] "2 can alternatively be immobilized in a polymeric or inorganic matrix which is insoluble in the substantially single liquid phase reaction system of this invention. For example, a double-layer hydroxy of the type described in Tetrahedron Letters, 8557 (1996) may be adapted to be used as a support with the phosphate-stabilized peroxotungstate compounds described herein. Also, ion exchange resins having quaternary ammonium functionality such as Amberlite IRA-400 (CI) can be used. The phosphate-stabilized peroxotungstate compounds described above are known in the art and can be synthesized by any suitable method such as, for example, the methods described in Salles et al., Inorganic Chemistry 33, 871-878 (1994).

For example, tungsten acid ("H2WO4") is combined with aqueous hydrogen peroxide and then phosphoric acid (H3 PO4) to give a precursor. Alternatively, H3 [PW12O40] • and H2O (available from commercial sources such as Janssen and Aldrich Chemical Company) were treated with phosphoric acid, then hydrogen peroxide, to give the precursor. The precursor is then reacted with a compound or substance capable of providing the desired "Y" cations such as an alkyl ammonium halide or the like. Said methods will give the compound in salt form. The acid formed can be generated by calcining the salt form of the compound under conditions effective to remove the ammonium alkyl. Heating the salt form of the compound to a temperature in excess of 400 ° C (preferably, not greater than 800 ° C) for a time from about 0.5 hour to 24 hours is generally effective for this purpose. Normally, calcination is preferred in the presence of oxygen. Other materials having catalytic activity in olefin epoxidation may also be present in the phosphate stabilized peroxotungstate compounds described above. For example, the phosphorus and tungsten containing catalyst described in the U.S. Patent Nos. Nos. 5,274,140, 4,562,276, 4,595,671 and 5,324,849 can be used in the mixture with the catalyst required by the process of the present invention. Olefins which may be subjected to the epoxidation reaction include, but are not limited to, unsaturated alkyl, alicyclic alkylaryl hydrocarbons, such as ethylene, propylene, butenes, pentenes and in general linear and branched mono- and di-olefins having up to 20 carbon atoms. carbon atoms, cyclohexene, norborene, limonene, camphene, vinyl cyclohexane styrene, indene, stilbene and the like; unsaturated alkyl halides such as allyl chloride; unsaturated acids and their esters such as acrylic acid, methacrylic acid, crotonic acid, oleic acid, methyl acrylate and the like; unsaturated alcohols and their esters such as allyl alcohol, methallyl alcohol and the like; unsaturated aldehydes; unsaturated ketones and the like. The olefin can be substituted with any substituents which does not interfere with the desired epoxidation reaction such as, for example, hydroxy, halogen, nitro, alkoxy, amine, carbonyl, carboxylic, ester, amide, or nitrile groups. Polyolefins such as dienes (e.g., 1,4-butadiene), trienes, either conjugated or not, can also be used successively. Acyclic alkenes containing from 3 to 10 carbon atoms are preferred for use. The epoxidation process of this invention is characterized by having a single liquid phase. That is, separate organic and aqueous layers that are not present. In addition, while the single liquid phase may contain water, the reaction system is predominantly compressed (e.g., greater than 50 weight percent) of one or more organic solvents (i.e., the liquid phase is "substantially organic"). ). While the olefin being epoxidized may function as a solvent when used in excess in relation to hydrogen peroxide, in preferred embodiments an additional organic solvent is present. The organic solvent is advantageously selected so that the hydrogen peroxide, water (is present) and olefin form a single homogeneous liquid phase when combined with the organic solvent under the epoxidation conditions. Generally speaking, relatively polar organic solvents that are miscible with water and / or hydrogen peroxide, to at least the same degree, are preferred for use. Such solvents include, for example, C1-C5 alcohols (e.g., methanol, ethanol, isopropanol, t-butyl alcohol, t-amyl alcohol, fluorinated alcohols), C2-C3 nitriles (e.g., acetonitrile). and C2-C6 ethers (e.g., tetrahydrofuran, glyme, dioxane, glycol ethers) The solvent preferably a liquid under the epoxidation conditions and could be non-reactive The epoxidation temperature is not critical, with the optimum temperature being influenced by, among other factors, the reactivity and nature of the olefin. Normally, however, temperatures between 0 ° C and 125 ° C are sufficient to achieve selective conversion of olefin to epoxide. Reaction times from a few minutes to a few hours are generally used. The pressure is also not critical, although with more volatile olefins such as propylene it will be desirable to use a sufficiently high pressure to maintain the desired olefin concentration in the liquid phase where the epoxidation takes place. Atmospheric pressures at 100 atmospheres are generally adequate for the operation of the present process. The catalyst is used in amounts between 0.001 and 1 g / tungsten atom per 1 mole of hydrogen peroxide, more preferably between 0.005 and 0.05 g / W atom per 1 mole of H2O2. The concentration of the olefin in a single-phase liquid reaction system is not critical, with concentrations from 1% to 50% by weight usually being selected for practical reasons. Similarly, the concentration of hydrogen peroxide is not referred to as critical. An advantage of the processes of this invention is that they are capable of providing high selectivity to the epoxide even when the H2O2 concentration is relatively low (eg, from 1 to 15 weight percent based on the total weight of the liquid phase ). The higher or lower concentrations can be used, however, if desired. The hydrogen peroxide can be derived from any suitable source such as, for example, air oxidation of an anthraquinone, secondary alcohol or the like. The hydrogen peroxide can be introduced as or produced by substances capable of generating hydrogen peroxide under the reaction conditions. For example, hydrogen peroxide can be generated in situ by the reaction of oxygen and hydrogen in the presence of a suitable catalyst. Olefin and hydrogen peroxide are used in substantially equimolar ratios. An excess or that lacks excesses with respect to one or other of the reactants does not interfere with the desired epoxidation. While molar ratios of olefin to hydrogen peroxide of between 0.1: 1 to 50.1 can be used, ratios are generally preferred between 1: 1 and 10: 1. EXAMPLES The procedure described in Salles et al., Inorg. Chem. 33, 871-878 (1994) is used to prepare the salt corresponding to (n-Bu N) 2 [PW2O? 3 (OH)]. The epoxidation of a variety of olefins using hydrogen peroxide is generally carried out using the following ratios of reagents: 18 mmoles olefin, 5% hydrogen peroxide and 5% water in an organic solvent (12 g, 18 mmoles H202 and 5% H20 in acetonitrile (42 g, 62 mmol of H2O2), 0.5 g (0.47 moles) of salt as catalyst The results obtained are shown in Table 1. The percentage of epoxide given is based on the conversion of hydrogen peroxide These results demonstrate that the remarkably high selectivity to epoxide is achieved by the process of the invention under mild reaction conditions in both protic and aprotic solvents, this is quite surprising in view of the fact that water is present in the same liquid phase as the olefin being reacted Normally, the water will deactivate the epoxidation catalysts or react with the epoxide to generate the by-product opening byproducts. rings, so they substantially reduce the performance of the desired epoxide.

Table 1 based on the conversion of hydrogen peroxide The catalytic activity of the acid formed of a peroxotungstate compound stabilized with phosphate investigated in the following manner. A 1 g sample of (n-Bu N) 2 [PW2O? 3 (OH)] is placed in an oven at 500 ° C under a slow fluid of air for 5 hours. Elemental analysis and IR spectroscopy indicate that all the tetrabutyl ammonium counterion can be removed. The solids were dissolved in 55 g of a 5% H 2 O 2 solution (in acetonitrile to 1,4-dioxane) with stirring at 60 ° C for 2 hours. The resulting catalyst solution is used to epoxidize propylene in acetonitrile under the conditions previously described. After 2.5 hours at 65 ° C, 90% of the hydrogen peroxide conversion and 64% of the selectivity for propylene oxide were observed.

Claims (20)

1. CLAIMS 1. An epoxidation process comprising contacting an olefin with hydrogen peroxide in a substantially inorganic liquid single phase reaction system in the presence of a catalytically effective amount of a compound in salt or acid form comprising species that correspond to [PW2O? 3 (OH)] "2 for a time and at an effective temperature to form an epoxide corresponding to the olefin 2. The epoxidation process according to claim 1, wherein the reaction system of a only substantially organic liquid phase comprises at least 10% by weight of water 3. The epoxidation process according to claim 1, wherein the liquid single-phase reaction system comprised of an organic solvent selected from the group consisting of of C 1 -C 4 alcohols, C 2 -C 3 nitrile, C 2 -C 6 ethers and mixtures thereof 4. The epoxidation process according to claim 1, in The compound is further comprised of a cation selected from the group consisting of H +, alkyl ammonium and combinations thereof. 5. The epoxidation process according to claim 1, wherein the olefin is an acyclic C3-C6 alkene. The epoxidation process according to claim 1, wherein the temperature is from 0 ° C to 125 ° C. ° C. 7. The epoxidation process according to claim 1, wherein the compound is soluble in the substantially single liquid phase reaction system. 8. The epoxidation process according to claim 1, wherein the compound is immobilized in a polymeric or inorganic matrix. 9. An epoxidation process comprising contacting an acyclic C2-C? 0 alkene, preferably C3-C10 with hydrogen peroxide in a liquid single-phase reaction system comprising less than 10% by weight of water and an organic solvent in the presence of a catalytically effective amount of a compound having an empirical formula Y2_x [PW2O? 3 (OH)] wherein Y is H +, alkyl ammonium, or combinations thereof, x = 0 when Y is a monocation, and x = 1 when Y is a dication at a temperature of 0 ° C to 125 ° C for an effective time to form an epoxide corresponding to the acyclic alkene of C2-C? Or, preferably of C3-C10 . 10. The epoxidation process according to claim 9, wherein the mono-olefin of C2-C? 0 is propylene. 11. The epoxidation process according to claim 9, wherein the organic solvent is selected from the group consisting of C? -C alcohols, C2-C3 nitriles, C2-C6 ethers, and mixtures thereof. 12. The epoxidation process according to claim 9, wherein Y is an alkylammonium cation corresponding to NR? R2R3R4 wherein R ,, R2, R3 and R4 are the same or different and are selected from C? -C24 alkyl groups? . The epoxidation process according to claim 9, wherein the compound is formed by reacting H3PW12O40, H3P04 and hydrogen peroxide to form a hammer and reacting the precursor with alkyl ammonium halide. 14. The epoxidation process according to claim 9, wherein the compound is formed by reacting tungsten acid, hydrogen peroxide and H3PO4 to form a percussor and reacting the precursor with alkyl ammonium halide. 15. The epoxidation process according to claim 9, wherein the compound is formed by reacting H3PW12O 0, H3PO and hydrogen peroxide to form a precursor, by reacting the precursor with an alkyl ammonium halide to form a compound in the form of salt, and calcining the compound to provide the compound in the acid form. 16. The epoxidation process according to claim 9, wherein the compound is formed by reacting tungsten acid, hydrogen peroxide and H3P04 to form a percussor, reacting the precursor with alkyl ammonium halide to form a compound in the form of salt and calcined the compound to provide the compound in the acid form. 17. The epoxidation process according to claim 9, wherein the water is removed to form the single-phase liquid reaction system during the epoxidation. 18. The epoxidation process according to claim 9, wherein the C3-C10 acyclic alkene is propylene. 19. The epoxidation process according to claim 9, wherein the amount of the compound is from 0.0001 to 1 g / tungsten atom per mole of hydrogen peroxide. The epoxidation process according to claim 9, wherein the organic solvent is selected from the group consisting of methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, t-butanol, acetonitrile, , 4-dioxane, tetrahydrofuran, glyme and mixtures thereof.